[BC] Slant wire feeds vs series fed

[Craig Healy]

I don't know if anyone else has addressed this as I'm wading through a month
of back list traffic..

I did try this, and it didn't work.  The combination of inside conductor and
outside tower acted as a big fat shorted coax stub.  No radiation to speak
of, and a really sharp Q.

Craig Healy
Providence, RI

----- Original Message ----- 
From: "Phil Alexander" <dynotherm at earthlink.net>
To: "Broadcasters' Mailing List" <broadcast at radiolists.net>
Sent: Thursday, January 26, 2006 9:47 AM
Subject: Re: [BC] Slant wire feeds vs series fed


> On 25 Jan 2006 at 8:34, Cowboy wrote:
>
> > On Wednesday 25 January 2006 08:08 am, Richard Fry wrote:
>
> > >Does anyone know of a shunt-fed, monopole installation where the feed
wire
> > >is inserted at the tower base, makes a 90-deg bend, and extends up in
the
> > >vertical plane on the tower vertical C/L to attach at the feedpoint?
> >
> >  While I don't know of any, it's something I've wanted to try for some
time.
> >  I really don't see much difference between that, and a standard skirt.
> >
> >  In this case, that the "outer conductor" is grounded rather than the
"inner
> >  conductor" should really make little difference in the current
distribution
> >  in the actual radiating element, the tower.
> >
> >  While I don't know of any coaxial sleeve antennae ever being used in
> >  the standard broadcast band, the principal is well understood in other
> >  services, and works quite well. ( though usually a full 1/2 wave
vertical
> >  dipole, rather than something shorter )
>
> This idea is quite a bit different from a 1/2 wave vertical dipole in
> that it has no insulator between upper and lower sections of the
> radiator if I understand what is being proposed.
>
> While I can see several advantages, to the "inside out" skirt, correctly
> tuning it might prove more difficult than tuning a conventional skirt
> and, a skirt permits considerably greater flexibility regarding inherent
> Q etc. as the support arm length is easily manipulated.
>
> This antenna should be an attractive one for Cowboy because more climbing
> probably would be involved for setting the feed attachment point. It seems
> to me you would want to tweak the attach point to achieve zero leg current
> at ground level.
>
> It looks like an interesting science project where we might learn a new
> trick or two, but if compared with a high power (six wire) skirt, I don't
> see a substantial advantage to offset the downside of higher cost, more
> difficult installation and reduced flexibility. It would be interesting
> to model this and compare, but my gut reaction is you will need a larger
> tower face to get the same bandwidth results as a conventional external
> skirt.
>
>
> Phil Alexander, CSRE, AMD
> Broadcast Engineering Services and Technology
> (a Div. of Advanced Parts Corporation)
> Ph. (317) 335-2065   FAX (317) 335-9037